This invention relates to biocompatible compositions and, more particularly, to compositions which are polymerizable or curable to form products which may be polymerized in situ in contact with living animal tissue, especially dentin, bone and living pulpal tissue, and which are particularly well suited for use as dental cavity liners, in pulp capping and pulpotomy, as endodontic and other dental filling materials, and as cements.
It has long been known that calcium hydroxide may serve as a protective barrier for pulpal tissue against the attack of acid from certain filling materials by acting as a neutralizing agent for the acids in cements and toxic elements eluted from filling materials. It also has been known for some time that calcium hydroxide has a stimulating effect on the formation of secondary dentin when the calcium hydroxide is applied near or on actual exposures of living pulp. This stimulation often is important as an adjunct to successful therapeutic treatment.
In the past, in order to place calcium hydroxide, or a calcium hydroxide former, such as calcium oxide, adjacent an exposed surface of living dentin or pulpal tissue, the calcium hydroxide was dispersed in water, or in an aqueous or organic solution of a film former, and brushed or otherwise applied over prepared surfaces of tooth cavities. These prior art aqueous dispersons apparently were innocuous and non-toxic to pulpal tissue and their use was reasonably successful. However, the use of aqueous dispersons which contain film formers was deficient in that a relatively long time was required for volatilization of the water and the resultant formation of the films. By contrast, the use of organic solvent systems, such as those systems comprised of calcium hydroxide, a film former and chloroform, required considerably less time for solvent evaporation and film formation. However, the use of such organic solvent systems posed problems because of the toxic effects of the solvents on pulpal tissue. Thus, although film formation was rapid, the use of organic solvents limited the application of organic solvent systems to instances where no involvement between the solvent and pulpal tissue was anticipated.
As one means of overcoming the deficiencies of some of the earlier aqueous and organic solvent systems, attempts were made to combine calcium hydroxide in certain systems that were usable as self-hardening pastes. One such self-hardening system is disclosed in U.S. Pat. No. 3,047,408 to Dougherty. In that patent there is described a dental composition comprised of a stoichiometric excess of calcium hydroxide mixed with an ester of a polyhydric alcohol and salicylic acid or its esters. The mixture reacts to form a rigid and permeable mass of calcium phenolate having available calcium hydroxide dispersed therein. Another system of this general type is disclosed in U.S. Pat. No. 4,240,832 to Jandourek. The Jandourek system comprises two pastes and is based upon calcium hydroxide and a condensate of an ester of salicylic acid and an aldehyde, such as formaldehyde or its oligomers.
For the most part, hardenable systems of the type disclosed in the Dougherty and Jandourek patents offer advantages over the earlier calcium hydroxide containing systems, and have been useful as dental cavity liners and pulp capping materials. However, under leaking fillings, the hardenable systems based on esters of salicylic acid tend to undergo hydrolysis which eventually may allow bacterial invasion, infection and secondary caries. These systems also exhibit relatively low compressive strengths, e.g., on the order of about 1500 to about 4000 psi, and relatively high water and acid solubility. Accordingly, when used as a cavity liner, a relatively thick layer of the material must be used so as not to crack under the pressures associated with the plugging of a dental filling material, for example, a dental alloy, onto the liner.
It also has been disclosed in UK Patent Application No. 2094326A to provide a restorative dental material including calcium hydroxide, a bisphenol-A glycidyl methacrylate prepolymer and a polymerization catalyst such as an organic peroxide and an amine. The materials disclosed in this UK application are self-hardenable compositions which must be stored in multiple packages until they are mixed and placed in a tooth preparation by a dentist.